Method of inhibiting growth of undesirable plants



United States 3,161,495 METHOD OF HNHHBETENG GROWTH OF UNDESERABLE PLANT Lee A. Miller, Kirltwood, Md, assignor to Monsanto (Zompany, a corporation of Delaware No Drawing. firiginal application Dec. 28, 1859, Ser. No. 862,4l95, now Patent No. 3,668,239, dated Dec. ll, 1%2. Divided and this application May 28, $62, Ser. No. 197,355

9 tllairns. (til. '71--2.)

C-SH ZOEOCOOY in which X is selected from the class consisting of -S-, O, and NH-, Y is an alkyl radical of from 1 to 5 carbon atoms, and Z is selected from the class consisting of Y, hydrogen and aryl radicals of from 6 to 10 carbon atoms.

The presently provided compounds are thus alkyl esters of acrylic acid wherein at the 3-position of the acrylic acid there'is a substituent which is a benzothiazolylthio radical, or a benzoxazolylthio radical or a benzimidazolylthio radical and wherein the 3-position may or may not have an alkyl or aryl substituent. Thus when Z of the above formula is hydrogen the compounds are allcyl 3-(2-benzothiazolylthio)acrylates, or 3-(2-benzoxayloylthio)acrylates or 3-(Z-benziniidazolylthio)acrylates.

The mercapto-substitu-ted polynuclear heterocyclic compounds which are presently employed are Z-mercaptobenzothiazole, 2-benzoxazolethio1 or Z-benzimidazolethiol.

The acetylenic carboxylates which are reacted with the above mercapto-substituted compounds are the allcyl esters of propiolic acid wherein the alkyl group contains from 1 to 5 carbon atoms and wherein there may be present at the 3-position of the propiolic acid an aliphatic or aromatic substituent. Examples of the presently useful acetylenic esters include the alkyl propiolates such as the methyl, ethyl, propyl, isopropyl, butyl, tertbutyl, isobutyl, amyl, isoamyl, or tert-amyl propiolates; the alkyl tetrolates such as the methyl, ethyl propyl, butyl or amyl tetrolates; the alkyl 2-pentynoates such as the methyl or butyl 2-pentynoate or the ethyl or isopropyl 4-ethyl pentynoate, the alkyl 2-hexynoates such as methyl or propyl 2-hexynoate; the aryl-propiolates such as ethyl or amyl phenylpropiolate or 2-, 3-, or 4-tolylpropiolate and methyl of butyl et-naphthylpropiolate; the alkyl Z-heptynoates such as ethyl or butyl Z-heptynoate or methyl, ethyl or isobutyl fi-me'thyl Z-heptynoate; the alkyl Z-Qctynoates such as methyl or propyl Z-octynoate, etc.

PatCflt 166 hldhtdd Patented Dec. 15, 1964 Examples of compounds prepared according to the presently provided process include, methyl, ethyl, or amyl 3- (Z-benzothiazolylthio)acrylate; ethyl, propyl or butyl (2- benzoxazolylthio)acrylate; butyl, isoamyl, or methyl 3-(2- benzimidazolylthio)acrylate; methyl or ethyl 3-(2-benzothiazolylthio)2-butenoate; methyl or butyl 3-(2-benzoxazolylthio)-2-butenoate; butyl or amyl 3-(2-benzimidazolylthio)-2-bu'tenoate; methyl or ethyl 3-(2-benzothiazolylthio)-2pentenoate, butyl or methyl 3-(2-benzoxazolyl- 'thio)-2-butenoate, amyl or butyl 3-(2-benzimidazolylthio)-2-pen-tenoate, methyl or ethyl 3-(2-benzoxazolylthio-Z-pentenoate, amyl or isopropyl I-S-(Z-benzrfithiazolylthio)-2-hexenoate, ethyl or methyl 3-(2-benzoxazolylthio)-2-hexenoate, amyl or methyl B-(Z-benzimidazolylthio)2-hexenoate, methyl or ethyl 3-(2-ben2othiazolylthio)-2-heptenoate, butyl or isopropyl 3-(2-benzoxazolylthio)-2-heptenoate, butyl or propyl 3-(2-benzothiaZoly1- thio -2-octeno ate, methyl or ethyl 3- (2-benzoxazolylthio 2-octenoate, methyl or ethyl 3-(2-benzothiazolylthio)-3- phenylacrylate, ethyl or isopropyl 3-(2-benzoxazolylthioJ-S-phenylacrylate, methyl or butyl 3-(2-b'enzothia- Zolylthio)-3-(2-tolyl)acrylate, ethyl or propyl B-(ZV-benzothiazolylthio)-3-(4-ethylphenyl)acrylate, methyl or ethyl 3-(2-benzothiazolylthio)-3-(fi-naphthyl)acrylate, ethyl or propyl 3-(2-benzoxazolylthio) 3 (wnaphthyhacrylatte, butyl or methyl 3-(Z-benzimidazolylthio)-3-(fi-naphthyl)- acrylate, etc.

Reaction of the present mercapto-substituted polynu clear heterocyclic compounds with the acetylenic esters takes place in the presence of basic or acidic catalysts. Basic catalysts useful inthe process include organic bases such as pyridine, the quaternary ammonium salts or bases such as trimethylbenzylammonium hydroxide, the alkali and alkali metal hydroxides or basically reacting salts thereof such as sodium, potassium, lithium, calcium, or magnesium hydroxide, carbonate or acetate; alkali or alkali metal alcoholates such as sodium methylate, etc,

in the presence of either the acidic or basic catalyst, and v in the presence of an inert diluent or solvent if desired, and allowing the resulting reaction mixture to stand at ordinary or increased temperatures until formation of the substituted olefinic ester has occurred. Useful solvents or diluents include benzene, xylene, dioxane, dichlorobenzene or hexane. Depending on the nature of the individual reactants and of the catalyst employed, the re action may occur under varying conditions of temperature and pressure. For optimum yields, it is advantageous to heat the reaction mixture attemperatures of, say, from approximately 60 C. to the refluxing temperature of the reaction mixture.

Inasmuch as molecular equivalents of the mercapto compound and the acetylenic ester are involved in the for mation of the presently provided substituted olefinic.

cess of either reactant may be employed since any unreacted material is readily separated from the product.

=3 It has been observed that in the reactions with the 2- benzimidazolethiol, the product is generally a mixture of the isomeric alkyl 3-(Z-benzimiadzolylthio)alkenoates and the alkyl 3-[ 1- (2-mercaptobenzimidazole) acrylates (II) CZ=CHCOOY It will be noted that (II) is formed by addition of the acetylenic ester at the imino radical of the thiol rather than at the mercapto radical. There is a preferential tendency for (I); so that (11) is present in minor amounts. While (II) may be removed from the reaction mixture by customary isolating procedures, e.g., fractional distillation, extraction or fractional crystallization, for most purposes it is unnecessary to provide (1) in a pure form. That it is because the crude (I), i.e., the reaction product which consists essentially of (I), is useful directly for a wide variety of industrial and agricultural purposes.

The presently provided alkyl 3-(2-benzothiazolylthio) alkenoates or 3-(2-benzoxazolylthio)alkenoates or the 3- (2-benzimidazolylthioalkenoates) and mixtures of the latter with the isomeric alkyl 3[1-(2-rnercaptobenzimidaz ole)] acrylates are stable, rather high-boiling viscous liquids or waxy to crystalline solids which are useful as lubricant additives, as vulcanization accelerators for rubbers, as copolymerizing monomers with vinyl compounds in synthetic resin and plastics manufacture, and as biological toxicants, e.g., as herbicides, bacteriostats, fungistats and insecticides. They are particularly valuable as preemergent herbicides in that they possess a specificity of effect so that they can be used as de-weeders without adversely affecting the crop. The benzothiazolylthio compounds are noteworthy in that they serve as crab grass eradicants without killing or substantially injuring the lawn grasses.

The invention is further illustrated by, but not limited to, the following examples:

Example 1 A mixture consisting of 8.4 g. (0.1 mole) of methyl propiolate and 50 ml. of benzene was added continuously to a mixture consisting of 16.7 g. (0.1 mole) of 2-mercaptobenzothiazole, 100 ml. of benzene and 1 ml. of 40% methanolic trimethylbenzylammonium methoxide. The reaction mixture, which darkened immediately, was heated at reflux for 12 hours. It was then dissolved in 100 ml. of ether and washed with two 50 ml. portions of saturated aqueous ammonium chloride. Evaporation of the organic solvents gave as residue a brown slurry. This was distilled through a small Vigreux column to give the substantially pure methyl 3-(2-benzothiazolylthio) acrylate, B.P. 171172 C./0.5 mm., M.P. 68-70 C., which analyzed 52.51% carbon and 3.60% hydrogen as against 52.56% and 3.61%, the respective calculated values.

Example 2 To a reaction vessel there was charged 15.0 g. (0.1 mole) of 2-benzimidazolethiol, 9.2 g. (0.11 mole) of methyl propiolate and 100 ml. of benzene. Upon addition of 1 ml. of trimethylbenzylammonium hydroxide catalyst to the mixture, darkening was noted and the temperature of the reaction mixture rose exothermally to about 45 C. In order to assure complete reaction the whole was then refluxed for 12 hours. At the end of that time the black reaction mixture was evaporated to give a 4 dark brown, pasty solid which could not be recrystallized from methanol. Difliculty in crystallization was due to the presence in the product of the following two isomers:

a CSI-l'.

Analysis of the pasty solid after washing it with three 50 ml. portions of hexane gave 56.62% carbon and 4.36% hydrogen, compared with 56.39% and 4.30%, the respectively calculated value for either isomer, i.e.,

Infrared analysis showed it to consist essentially of (I), i.e., methyl 3-(2-benzimidazolylthio)acrylate and a minor amount of (II), i.e., methyl 3-[1-(2-mercaptobenzimidazole) ]acrylate.

Example 3 When a catalytic quantity (1 ml.) of trimethylbenzylammonium hydroxide was added to a mixture consisting of 15.1 g. (0.1 mole) of 2-benzoxazolethio, 9.2 g. (0.11 mole) of methyl propiolate and ml. of benzene, the mixture blackened and spontaneously warmed to 45 C. The whole was then heated at reflux for 12 hours. Upon evaporation of the solvent there was obtained a black oil which solidified upon standing. Repeated recrystallization from methanol gave the substantially pure methyl 3-(2-benzoxazolylthio)acrylate, buff needles, M.P. 93.5- 95.0 C., which analyzed 56.14% carbon and 4.10% hydrogen compared with 56.16% and 3.86% the respective calculated values for C H NO S. Infrared analysis showed the presence of the -C=N structure at 1590 cmf the presence of C--0-ester structure at 1230 and 1220 cmr and the presence of 4 adjacent protons at 755 and 750 cnL- Example 4 This example shows evaluation of the methyl 3-(2- benzothiazolylthio)acrylate of Example 1 as a preemergent herbicide. Briefly, the chemical is applied in spray form to soil seeded to representative grasses and broadleaf plants. 7

Aluminum pans, 13" x 9" x 2", were filled with a good grade of top soil which had been screened through a /4 wire mesh and mixed with sand in a preparation of two parts of the top soil to one part of the sand. The soil surface was then compacted to a depth of from the top of the pan. Twenty seeds each of morning glory, wild oats, crab grass, rye grass, radish, sugar beet, barnyard grass, wild buckwheat, and pigweed were then scattered on the soil surface and covered with soil to the pan top.

The present herbicidal solution was prepared by dissolving 0.4 g. of the methyl 3-(2-benzothiazolylthio) acrylate in 22 cc. of acetone. Ten ml. of this solution was diluted with water to 30 cc. Application of this quantity of the solution to said pans is calculated to correspond to the use of 25 lbs. of the test compound per acre. The planted pans were then placed in an exhaust hood and sprayed first with 30 cc. of an aqueous solution of a liquid fertilizer and 0.1% solution of octamethyl pyrophosphoramide. The liquid fertilizer was employed to give a uniform nutrition level and the amide was employed to prevent insect injury. Two pans were then respectively sprayed with the 25 lb. per acre solution of the test compound. One of the pans which had been planted and treated with the liquid fertilizer and octamethyl pyrophosphcramide in the same manner was set aside to be used as a blank. The three pans Were then placed in /2" of water and allowed to absorb moisture through perforated bottoms until the soil surface was completely moist. The pans were then transferred to a wet sand bench in the greenhouse, and maintained there for ten days under ordinary conditions of sunlight and watering.

Observation of the pans at the end of that time showed that those which had been sprayed with the 25 lbs. per acre solution of the methyl 3-(2-benzothiazolylthio) acrylate showed complete to very pronounced suppression of crab grass and pigweed; however, the radish, morning glory, wild buckwheat, wild oats, rye grass and bamyard gnass had emerged and showed no evidence of phytotoxicity. Also, all of the types of seeds which had been planted in the pan which had not been sprayed with the methyl 3-(2-benzothiazolylthio) acrylate had emerged and the plants were in excellent condition. Accordingly, when used at the rate of 25 lbs. per acre, the methyl 3- (2-benzothiazolylthio)acrylate is an unusually effective preemergent herbicide in that it prevents emergence and growth of crab grass and pigweed without having any adverse effect on wild oats, rye grass, and mustard.

Employing the same testing procedure, but using morning glory, wild oat, brome grass, rye grass, radish, sugar beet, foxtail, crab grass, pigweed, soybean, wild buckwheat, tomato and sorghum as the test seeds, the methyl 3-(2-benzoxazolylthio)acrylate of Example 3 was also found to give complete to very pronounced suppression of crab grass and pigweed. However, with this compound there was not the pronounced specificity which was exhibited by the methyl 3-(2-benzothiazolylthio) acrylate; for in addition, wild oat and rye grass were pronouncedly suppressed brome grass and sugar beets were moderately injured, and morning glory, foxtail, and soybean were slightly injured. There was no effect on radish, wild buckwheat, tomato and sorghum. Accordingly, the methyl 3-(2-benzoxazolylthio)acrylate is a preemergent herbicide which is effective against the narrow leafed plants, generally, while not substantially harming the broad leaf plants. I

When employing the same testing procedure with the product of Example 2, i.e., the mixture of methyl 3-(2- benzimidazolylthio)acrylate and methyl 3-[-(2-mercaptobenzimidazole)]acrylate completely different results were obtained. This product was found to inhibit germination and growth of several broad leaf plants, e.g., morning glory, sugar beets and tomato, while not at all affecting wild oat, brome grass, rye grass, foxtail, and crab grass.

While the present compounds are advantageously employed as herbicides by incorporating them into an emulsion or solution, they may also be incorporated into solid carriers such as clay, talc, pumice or bentonite to give compositions which may be applied either to infested areas or to locale which may be subject to infestation. They may also be dissolved in liquefied gases such as the fluorochloroethanes or methyl chloride and applied from aerosol bombs containing the solution.

This application is a division of my copending application, Serial No. 862,095, filed December 28, 1959, now U.S. Patent No. 3,068,239, December 11, 1962.

What I claim is:

l. The method of treating soil for the purpose of inhibiting the growth of undesired plant growth which comprises the addition to said soil of a herbicidal quantity of a composition comprising as the essential ingredient a compound of the formula in which Y is alkyl of from 1 to 5 carbon atoms, and Z is selected from the class consisting of alkyl of from 1 to 5 carbon atoms, hydrogen and hydrocarbon aryl of from 6 to 10 carbon atoms.

3. The method of claim 1 wherein the essential ingredient has the formula in which Y is alkyl of from 1 to 5 carbon atoms, and Z is selected from the class consisting of alkyl of from 1 to 5 carbon atoms, hydrogen and hydrocarbon aryl of from 6 to 10 carbon atoms.

4. The method of claim 1 wherein the essential ingredient has the formula in which Y is alkyl of from 1 to 5 carbon atoms, and Z is selected from the class consisting of alkyl of from 1 to 5 carbon atoms, hydrogen and hydrocarbon aryl of from 6 to 10 carbon atoms.

5. The method of inhibiting the growth of undesirable plants which comprises treating the soil, in the area where such plant growth is not desired, with a growthinhibiting quantity of a preemergent herbicidal composition comprising as the essential ingredient a compound of the formula o-s-cz=ono 0 OY in which X is selected from the class consisting of S--, -O- and -NH, in which Y is alkyl of from 1 to 5 carbon atoms, and Z is selected from the clas consisting of alkyl of from 1 to 5 carbon atoms, hydrogen and hydrocacrbon aryl of from 6 to 10 carbon atoms. 0

6. The method of claim 5 wherein the essential ingredient is methyl 3-(2-benzothiazolylthio)acrylate.

7. The method of claim 5 wherein the essential ingredient is methyl 3-(2benzimidazolylthio) acrylate.

8. The method of claim 5 wherein the essential ingredient is methyl 3-(2-benzoxazolylthio) acrylate.

9. The method of inhibiting the growth of crab grass and pigweed, which comprises treating the soil, in the area where such plant growth is not desired, with a growth-inhibiting quantity of a preemergent herbicidal composition comprising as the essential ingredient methyl 3- (2-b enzothiazolylthio) acrylate.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF TREATING SOIL FOR THE PURPOSE OF INHIBITING THE GROWTH OF UNDESIRED PLANT GROWTH WHICH COMPRISES THE ADDITION TO SAID SOIL OF A HERBICIDAL QUANTITY OF A COMPOSITION COMPRISING AS THE ESSENTIAL INGREDIENT A COMPOUND OF THE FORMULA 